Ryan Welcher

This is a simple plugin that helps to clean up the admin side of WordPress by only showing the currently logged in user’s content the Post/Page/Media pages.
For the Media list, you can provide a list of user ID’s who’s Media will also be available to logged in users. It is highly recommended to create a user for this purpose.
Credits
This plugin was inspired by an article by <a href="http://premium.wpmudev.org/blog/author/pollyplummer/" rel="nofollow ugc">Sarah Gooding</a> on <a href="http://premium.wpmudev.org/blog/how-to-limit-the-wordpres-posts-screen-to-only-show-authors-their-own-posts/" rel="nofollow ugc">wpmudev</a> and uses portions of that code. Please see the source code for further details.

Restrict User Content

Limits Post/Pages/Media admin screens to only display the current user's content. Media can be shared by providing an ID list.

PeteHoliday

kimedia

This is a simple plugin to allow for restricting access to content.
Users may be members of multiple groups. Multiple groups and multiple individual users may be allowed to view each 
post. Overlaps are ignored — if the user is a member of any group that is allowed to view the post, that user will 
be able to view it.

Custom Post Type Privacy

Stable Tag 0.3 Custom Post Type Privacy allows WordPress authors to grant access to users and groups of users across all posts, pages and custom post …

Restrict User Content vs Custom Post Type Privacy